1. Field of the Invention
The present invention relates generally to gas turbine engine, and more specifically for a turbine rotor blade with cooling air inlet holes connected to a live rim cavity.
2. Description of the Related Art including information disclosed under 37 CFR 1.97 and 1.98
In a gas turbine engine, such as a large frame heavy-duty industrial gas turbine (IGT) engine, a hot gas stream generated in a combustor is passed through a turbine to produce mechanical work. The turbine includes one or more rows or stages of stator vanes and rotor blades that react with the hot gas stream in a progressively decreasing temperature. The efficiency of the turbine—and therefore the engine—can be increased by passing a higher temperature gas stream into the turbine. However, the turbine inlet temperature is limited to the material properties of the turbine, especially the first stage vanes and blades, and an amount of cooling capability for these first stage airfoils.
The first stage rotor blade and stator vanes are exposed to the highest gas stream temperatures, with the temperature gradually decreasing as the gas stream passes through the turbine stages. The first and second stage airfoils (blades and vanes) must be cooled by passing cooling air through internal cooling passages and discharging the cooling air through film cooling holes to provide a blanket layer of cooling air to protect the hot metal surface from the hot gas stream.
Turbine rotor blades are typically secured to a rotor disk using a fir tree root configuration that slides within a slot formed within the rotor disk. Cover plates are secured over both sides of the rotor disk in the area where the fir tree and slots are located to both protect the rotor disk from high temperatures and to seal the small gaps or spaces formed between the fir tree and the slot. FIG. 1 shows a prior art turbine rotor blade and rotor disk configuration in which the blade 11 is secured within a slot of a rotor disk 14, the blade includes a platform 12 with a labyrinth seal 15 on one side, two cover plates 13 are secured onto the sides of the rotor disk 14 with the forward cover plate 13 having a cooling air inlet hole 16 to supply cooling air form the blade through a live rim cavity 17. The live rim cavity 17 is formed between the bottom of the slot and the bottom of the root of the blade 11.
FIG. 2 shows a side view of the rotor blade and slot configuration with the live rim cavity 17 formed between a bottom of the blade root 18 and the rotor disk 14. FIG. 3 shows a view of the bottom of the blade root 18 with the aft side cover plate 13 closing off the live rim cavity and three cooling supply inlet holes 19 that open into the live rim cavity 17. The arrows represent the cooling air flow from the cover plate cooling inlet holes and into the blade supply cooling supply inlet holes 19. In this embodiment, three cooling supply inlet holes 19 are used. However, more or less than three holes can be used without departing from the spirit or scope of the present invention.
One of the major problems with the prior art design for the blade root cooling air supply holes is the pressure losses or inlet losses associated with this design. These losses result in lower pressure available for cooling of the blade and results in a higher pressure to provide adequate cooling flow. The cooling air entering the live rim cavity has a velocity of around 0.1 Mach number. With this high velocity, a high cross flow effect occurs due to the cooling air changing direction from axial flow to a radial flow into the blade root cooling supply channels. FIG. 4 shows a graph of the entrance loss (k) versus the feed channel Mach number for each of the three feed holes 19 in which each live rim cavity is designed with a constant Mach number. FIG. 5 shows a cross section view of the live rim cavity and the three feed holes 19 with the first feed holes being the L/E feed hole, the middle feed hole being the M/C feed hole and the last feed hole being the T/E feed hole. As shown in the graph of FIG. 4, the entrance loss (k) decreases as the feed channel Mach number increases.